Reply to "1970 Boss 351"

I don't believe DeTomaso's horsepower claims were accurate. Just sales BS. Unless they were referring to DIN measurements as opposed to SAE measurements or some other kind of shenanigans.

If the exhaust back pressure was significantly lower, or if the DeTomaso headers actually scavenged better than the cast iron manifolds, the carburetor would have required re-jetting. This was not the case, Pantera carburetors & Mustang carburetors are interchangeable. Just looking at the DeTomaso headers I can see the primaries and the tailpipes are much too small for a Cleveland. The GTS exhaust system was an honest attempt to build a better exhaust system, but the Ford spec system was all show and no go; I'll bet the exhaust back pressure of the Ford spec Pantera exhaust system was identical to the exhaust back pressure of a Mustang equipped with a 351C 4V. Dan is absolutely right that a good exhaust system can be worth 30 to 50 BHP with a 351C 4V. The 351C 4V is a 520 BHP race motor, those heads were not designed to work well with a restrictive exhaust system.

While we're on the subject of sales BS, the 1970 M code motor was rated at 11.0:1 compression ratio by Ford, but was in reality only 10.0:1

-G